Battery charging apparatus with timing device



Dec. 9, 1969 .1. H. scHAEFER 3,483,461

BATTERY CHARGING APPARATUS WITH TIMING DEVICE Filed Nov. 22, 196'? NVEWOR. c/osgpf/ A. Sauf/FH? United States Patent O 3,483,461 BATTERY CHARGING APPARATUS WITH TIMING DEVICE Joseph H. Schaefer, Minnetonka, Minn., assignor to Marquette Corporation, Minneapolis, Minn., a corporation of Delaware Filed Nov. 22, 1967, Ser. No. 685,040 Int. Cl. H02j 7/04, 7/16 U.S. Cl. 320--31 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION In charging a battery, it is very desirable that the charging time bear a predetermined relation to the condition of the battery to be charged. One way in which to measure this condition is to place the battery under load and then measure the voltage across it. It has been proposed to employ a voltmeter for this purpose and to employ a timer having a variable impedance which is adjusted in accordance with the adjustment of the timer. The variable impedance is connected to the battery voltage and to the Voltmeter in such a way that the effect of the battery voltage on the voltmeter is modied in accordance with the setting of the variable impedance. By adjusting the timer until the voltmeter reads a predetermined value, the timer tends to be set for a timing period corresponding to the battery voltage under load. When the voltmeter reading reaches this predetermined value, a manually operable switching device is then actuated to disconnect the load from the battery and to initiate the charging operation which lasts for the time period determined by the setting of the timer. Such an arrangement is shown in the Pugh Patents 2,431,- 707 and 2,432,609.

The drawback of these previous arrangements is that they require the operator to observe the meter reading and to actuate a manually operable switching device when the correct meter reading is obtained. Furthermore, any variation in the calibration of the voltmeter will remain undetected and will affect the timing period for which the timer is set.

SUMMARY OF THE INVENTION In the present arrangement, when the timer is adjusted to the proper point, a switching device is automatically operated to initiate the charging operation. Since it is desirable to make such a test with the load resistance connected across the output terminals, the operation of the switching device, for example, a relay, also disconnects this load resistance so that the load resistance will not be present during the charging operation. A further very important feature of my invention is that a source of constant reference voltage, such as a Zener diode, is employed and a portion of the voltage across the battery to be charged is compared with this standard voltage. The resultant voltage is then used to control an electronic circuit which, in turn, controls the switching device. Because of the fact that the reference voltage is constant, the timing period which is set is not affected by any change in the calibration of a meter.

Another feature of my invention is I employ a transistor ice for controlling the switching device which in turn initiates the charging operation. By using a transistor which does not have a warmup time, it is possible to very quickly set the timer into the correct position and have the transistor immediately respond to the timer reaching its proper position.

A further feature of my invention is that if the timer is adjusted to the end of its range of movement corresponding to the maximum charging period and the voltage comparing circuit has not resulted in the switching apparatus being operated, as could happen with a heavily discharged battery, the switching device is operated independently of the voltage comparing circuit to initiate the charging operation.

BRIEF DESCRIPTION OF THE DRAWING The single gure of the drawing shows my improved battery charger in schematic form, the charging apparatus being shown as connected to a battery to be charged.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, the charging apparatus is shown as being located within a housing shown in dotted lines. The charging apparatus has output terminals 11 and 12 which are shown as connected to a battery 13 to be charged. The apparatus also has input terminals 14 and 15 which are adapted to be connected to a suitable source of commercial power, such as power leads 16 and 17.

Referring to the charging apparatus, the charging current is derived from a step-down transformer 19 having a primary winding 20 and a low voltage secondary winding 21. The left-hand terminal of the primary winding 20 is connected by conductors 22 and 23 to the input terminal 15, which, in turn, is connected to power supply line 17. The primary winding has 4 taps, 27, 28, 29 and 30, one or the other of which is selectively engaged by a switch blade 31, which, in turn, is connected through various switches, to be presently described, to the other input terminal 14, which, in turn, is connected to the other line wire 16. The selector switch 31 is placed in various positions depending upon the charging rate desired, it being obvious that the secondary voltage produced by secondary winding 21 is determined by the position of switch 31.

The secondary winding 21 is center tapped at 36 and is connected through a conductor 37, a switch 38 within a polarity protector 39, and conductor 40 to a negative bus conductor 41 leading to the output terminal 11. The opposite terminals of secondary winding 21 are connected to rectifying diodes 4Z and 43 through a positive bus conductor 44 leading to the other output terminal 12.

Referring to the polarity protector 39, such polarity protectors are old in the art, a typical unit of this type being shown in the St. John Patent 3,308,365, granted Mar. 7, 1967. The function of such a polarity protector is to sense the polarity of the Voltage of the battery connected across output terminals 11 and 12 and to cause closure of switch 38 only when the terminals 11 and 12 are connected in the proper polarity lmanner to the battery 13. Since such polarity protectors are old, the details of unit 30 are not disclosed and will not be discussed herein.

It will be readily apparent from the above description that when the primary winding 20 of the transformer 19 is energized and the output terminals 11 and 12 are connected in the proper polarity manner to the battery 13 so as to cause closure of switch 38, a D.C. voltage will be applied to the terminals of the battery 13 to charge the same. As mentioned above, the lower bus conductor 44 will be positive, and the upper bus conductor 41 will be negative.

As pointed out previously, the apparatus of the present invention employs a timer for determining the length of time during which a charging operation takes place. This timer is of the type which can be set for any desired timing period. The timer is generally designated by the reference numeral 46 and has a shaft 47 (shown schematically in dotted lines), which acts both as an output shaft and a setting shaft. This shaft 47 is connected to a timer motor 45 which can be either electrically operated or in the form of a spring-wound mechanism which serves to return the shaft 47 to its starting position after the motor 48 has been set. When the motor is an electrical motor, the setting mechanism will operate the shaft 47 through a slip connection, the motor 45 thereupon operating to move the shaft 47 back to the starting point. The shaft 47 is set by knob 48 which has a pointer thereon cooperating with a scale 50 having suitable indicia thereon to indicate the length of the timing period. The shaft 47 also carries cams 49, 51, 52, 53 and 5-4, these cams cooperating with switches 55, 56, 57, 58 and 59 respectively. All of these switches except switch 55, are held open by their respective cams when the timer is in the zero or off position shown in the drawing. Upon knob 48 being rotated in a clockwise direction to set the timer 46, the movement of shaft 47 and the resulting movement of cams 51, 52, 53 and 54 cause the corresponding switches 56 through 59 to close. These switches remain closed until the timer returns to its off position. Switch 55 is also open when the timer is in the zero or off position, being biased to this position by any suitable means, not shown. When knob 48 is rotated to the end of its range of movement, the lobe on cam 49 is effective to close switch 55 while the timer is in its extreme position for the maximum charging time. The switch 59 should be of a type designed to carry very heavy currents. Switch 59 may, for example, be a heavy duty snap switch controlled by cam 54. Or switch 59 may control an awaiting heavy duty relay.

Also associated with the timer is a rheostat 62. This rheostat comprises a resistor 63 and a slider 64 movable thereover. The slider 64 is connected through a suitable mechanical connection 65 to the shaft 47 of the timer.

When the timer is in the zero or off position, the slider 64 is at the bottom of slider 63. When the timer is set so as to be moved away from its off position, the slider 64 is moved upwardly to a position dependent upon the setting of the timer.

A switching device such as a relay 66 is employed to control the energization of the primary winding 20 of transformer 19 as well as the energization of other elements of the apparatus. This relay comprises a relay coil 67 and a plurality of switch blades 68, 69, 70, 71 and 72. Switch blades 68, 69, and 70 cooperate with switch contacts 73, 74, 75, being normally separated therefrom when the relay is deenergized. When the relay coil of 67 is energized, switch blades 68, 69 and 70 move into engagement with contacts 73, 74 and 75 respectively. Switch blades 71 and 72 are normally in engagement with contacts 77 and 78, being separated therefrom upon energization of the relay coil 67. The relay is designed so that upon energization of relay coil 67, switch blade 72 Separates rst from contact 78, switch blade 68 next engages contact 73, switch blade 71 next separates from contact 77, and switch blades 69 and 70 then engage contacts 74 and 75. This is accomplished by the use of overlapping contacts or any of the other expedients cornmonly employed in the relay art to insure operation of the relay switches in a desired predetermined order.

The energization of the relay coil 67 is controlled by a PNP transistor 80, the emitter-collector contacts of which are connected in series with relay coil 67.

Power for the control circuit including transistor 80 is supplied by a step-down transformer 85 having a primary winding 86 and a low Voltage secondary winding 87. The upper terminal of primary winding 86 is connected through a switch `88 to the input terminal 14. The lower terminal of primary 86 is connected through a conductor 2.3 to the other input terminal 15. The switch 88,

a normal on-oif switch, is closed when it is desired to operate the apparatus.

The secondary winding 87 is connected through a diode 90 to the terminal 91. The lower terminal of secondary winding 87 is connected to a terminal 92. Connected between terminals 91 and 92 is a suitable lter capacitor 93. It will be understood that the diode 90 tends to rectify the output of secondary 87 so that a D.C. voltage appears between terminals 91 and 92, the terminal 92 being positive with respect to the terminal 91.

An indicating light is indicated by the reference numeral 95. This light will be located on the front of the panel of the apparatus so it can be visible to the operator. As will be explained in more detail later, signal light 95 is energized whenever the relay 66 is energized and serves to indicate the initiation of the charging cycle.

A Zener diode 96 is connected in series with the resistor 63 of potentiometer 62. As will be explained in more detail, when the timer is not in its zero position, the Zener diode 96 and resistor 63 of rheostat 62 are connected in series across the output terminals 11 and 12.

A lpotentiometer 97 includes a resistor 98 and a slider 99. Theresistor 98 of potentiometer 97 is connected between the slider 64 of potentiometer 62 and the positive bus conductor 44, this connection being through relay switch 71 and Contact 77. The slider 99 is in turn connected through another Zener diode 101 to the base of transistor 80.

The reference numeral indicates a load resistor which, as will be pointed out in more detail later, is connected between the output terminals 11 and 12 during the period of time in which the timer 46- is being set.

A center scale ammeter 104 may `be connected in the negative bus conductor 41 in series with the battery 13.

OPERATION The various elements are shown in the drawing in the position which they assume when the charger has rst been connected to a battery and the input terminals 14 and 15 have been connected to the power lines 16 and 17. When it is desired to initiate the charging operation, the manual switch 88 is closed to supply power to the primary winding 86 of transformer 85. This causes energization of primary 87 to cause a unidirectional voltage to appear between the terminals 92 and 91.

The knob of the timer 46 is now turned in a clockwise direction. The initial turning of this knob and the resultant rotation of shaft 47 causes rotation of the cams 51 through 54 and the resultant closure of switches 56 through 59.

Closure of switch 59, which is in series with relay switch blade 72 and contact 78, results in the load resistor 105 being connected across the output terminals 11 and 12 and hence across the battery 13 to be charged. This circuit may be traced from the positive conductor 44 through conductor 110, relay switch blade 72, contact 78, conductor 111, load resistor 105, conductor 112, and cam switch 59 to the other bus conductor 41 leading through ammcter 104 to the negative output terminal 11. The load resistor 105 is now connected across the battery 13 so as to enable a voltage measurement of the battery under load to be obtained. As pointed out above, switch 59 is designed to carry the large current that will ow through resistor 105.

The closure of timer switch 57 causes Zener diode 96 and the resistor 63 of potentiometer 62 to be connected in series between the output bus conductors 41 and 44, this circuit being as follows. from bus conductor 44, Zener diode 96, conductor 115, resistor 63, conductor 116, timer switch 57, and conductor 117 back to the other bus con ductor 41 in series with ammeter 104. The voltage drop across the Zener diode 96 is a constant voltage drop, regardless of the voltage across the battery 13. Thus, any variation in the voltage drop across battery 13 with respect to the iixed voltage across the Zener diode 96 appears as a variation in the voltage drop across resistor 63. A

variable portion of the voltage across resistor 63 is tapped off iby slider 64. The voltage between the bus conductor 44 and slider 64, which voltage includes the voltage drop across the Zener diode and the voltage existing between the lower end of resistor 63 and slider 64, is applied across resistor 98 of potentiometer 97, the lower end of resistor 98 being connected to the bus conductor 44 and the upper end being connected through switch blade 71 and switch contact 77 to slider 64. A variable portion of the voltage appearing across resistor 98 is tapped olf by the adjustable slider 99 and applied between the base and emitter of transistor 80 through Zener diode 101. It will be noted that the slider 99 is connected through Zener diode 101 to the base of the transistor 80. The emitter of the transistor 80 is connected through conductor 120, timer switch 56 and conductor 121 to the lower bus conductor 44. The voltage which is thus applied between the base and emitter of transistor 80 is a selected portion of the voltage appearing rbetween the slider 64 and bus conductor 44. This voltage in turn, as pointed out above, includes the fixed voltage drop across Zener diode 96 and a variable voltage dependent upon the voltage difference between the voltage actually existing across battery 13 and the xed voltage across Zener diode 96. The polarity of the voltage thus applied between the base and emitter of transistor 80 is such as tends to cause the base to become negative with respect to the emitter and hence to cause the transistor 80 to become conductive.

Initially, with the timer in the zero position, as pointed out above, the slider 64 is in its lowermost position s0 that the only voltage applied between the base and emitter of transistor 80 is ya selected portion of the voltage drop across the Zener diode 96. The slider 99 is so adjusted that this voltage is insuicient to cause the transistor to become conductive. As the knob 40 of the timer is rotated in a clockwise direction, the slider 64 is moved upwardly along resistor 63 to apply an increasing proportion of the voltage across battery 13 between the base and slider 99. After the knob 48 has been turned clockwise to a position corresponding to the desired charging time, the voltage applied between the slider 99 and base and emitter becomes suiiiciently high to cause Zener diode 161 to conduct to apply the voltage between the base and emitter so as to cause transistor 80 to be suiciently conductive to cause energization of relay 66. It 'will be obvious that the lower the voltage of the battery 13, the more the knob 48 must be turned. Thus, the lower the voltage of the battery 13, the greater will be the charging time selected.

When transistor 80 becomes sufliciently conductive by reason of the timer having been set for the desired timing period, dependent 4upon the condition of battery 13, an energizing circuit will be established to relay winding 67 from terminal 92 through conductor 121, timer switch 56, conductor 120, transistor 80, and relay winding 67 to the other terminal 91. This will cause relay 66 to pull in, thus causing switch blades 68, 69 and 70 to move into engagement with the contacts 73, 74 and 75, respectively, and switch blades 71 and 72 to move out of engagement with contacts 77 and 78.

The separation of switch blade 72 from contact 78, which occurs before switch blade 71 separates from contact 77 results in disconnecting the load resistor 105 from across the output terminals 11 and 12. This is desirable since the load resistor 105 should not be connected across the battery during the charging period, the sole function of the load resistor being to simulate the load condition during the measurement of the voltage across the battery 13.

The movement of switch blade 70 into engagement with contact 75 will establish an energizing circuit to the primary winding 20 of transformer 19 `as follows: from the upper terminal of primary 86, which as previously explained is connected to the input terminal 14, through conductor 124, timer switch 58, conductor 125, contact '75, switch blade 70, conductor 126, switch blade 31, the selected one of contacts 27, 28, 29 and 30, the selected portion of primary winding 20, and conductors 22 and 23 back to the other input terminal 15. The secondary 21 of transformer 19 will now be energized to apply charging current to the battery 13.

The closure of switch blade 68 with contact 73 completes a short circuit around the transistor to establish a holding circuit for the relay 67 independently of transistor 80. The separation of switch blade 71 from contact 77 disconnects the voltage across the battery from the base of the transistor 80 so that transistor 80 now becomes non-conductive. In view of the holding circuit discussed above, the relay winding 67 remain energized.

The closure of switch blade 69 with contact 74 will establish an energizing circuit `for indicating light from the lower positive terminal 92 of the D.C power supply, through conductor 127, switch blade 69, contact 74, conductor 128, indicating light 95, and conductor 129 back to the negative terminal 91 of the D.C. power supply. This will cause the indicating light 95 to be illuminated to indicate that charging has been initiated. It also serves as a warning to the person setting the timer 46 that the timer has been properly set and that the knob 48 should not be adjusted further.

In the above description, it has peen assumed that the battery voltage was suiciently large that the voltage between slider 99 and the base of transistor 80 reached such a value as knob 48 is adjusted to cause Zener diode 101 to become conductive to cause transistor 80 to become conductive to result in energization of the relay winding 67. In the case of a highly discharged battery, this condition may never be obtained, however. To make it possible to initiate a charging operation under these conditions, l provide the timer switch 55 which, as previously explained, is closed when knob 48 is adjusted to provide for the maximum charging time. When timer switch 55 is closed, the transistor 80 is shunted and an energizing circuit for relay coil 67 is established from the positive terminal 92 through conductor 121, conductors 120 and 131, timer switch 55, conductor `132, and relay winding 67 to the negative terminal 91.

When the relay winding 67 is energized by closure of timer switch 55 in the manner described above, the pulling in of the relay and the resultant engagement of switch blade 68 with contact 73 will establish the `above traced holding circuit for relay coil 67 so that as the timer returns towards its starting position and timer switch 55 again opens, the relay will remain energized.

The timer now continues to run for a timing period determined by the extent to which the timer 46 has been set. At the end of this timing period, the timer returns to the position shown in the drawing in which timer switches 55, 56, 57, 58 and 59 are all open. The opening of timer switch 58 interrupts the previously traced circuit to the primary winding 20 to terminate the charge operation.

The opening of the timer switch 56 results in deenergization of the relay winding 67, since the timer switch 56 is in series with relay coil 67. The deenergization of the relay 67 will cause the switch blades 68, 69, 70 and 71 to assume the position shown in the drawing. The separation of switch blade 69 from contact 74 as the result of the deenergization of relay 67 extinguishes the indicator light 95 to indicate to the operator that the timing operation is complete. While the re-engagement of switch blade 72 with contact 78 establishes part of the circuit for the load resistor 105, the load resistor 10 is not reconnected across the battery 13 because of the fact that the timer switch 59 is now open.

It will be apparent from the above description that with my apparatus, the setting of the timer automatically initiates a charging operation without further steps being taken. In some cases, it may be desirable to set the charging rate by observing the reading of ammeter 104l and adjusting the switch 31 after the charging has started. Ex-

cept for this one step, however, the operation following the turning of the knob is completely automatic. Furthermore, because of the fact that the voltage across the battery is compared with the voltage drop across the Zener diode which is constant, there is no problem of recalibration of the equipment being periodically necessary. Because of the use of a transistor as .a current amplifying device, the apparatus is immediately ready for operation as soon as the main switch 88 is closed. The operator need merely close the switch and turn the knob until light 95 comes on. He then knows that the charging operation has been automatically started and that the timer has been set for a charging period which is properly related to the condition of the battery 13.

Furthermore, I have provided for initiating the charging operation even when the battery voltage is so low that it is impossible for the voltage comparing circuit including Zener diode 96 to initiate the charging. This is accompilshed by the auxiliary timer switch 55. Under these conditions, the charging period is the maximum provided for by the timer. It is understood that if at the end of this charging period, the battery is not fully charged, the knob 43 of the timer can again be rotated to establish an additional charging period, the length of which will be dependent upon the voltage then existing across battery 13 when under load.

While I have described a specific embodiment of my invention, it will be `understood that this is for purposes of illustration only and that my invention is to be limited solely by the scope of the appended claims- I claim as my invention:

1. In a battery charging apparatus, means for producing a charging current including input terminals adapted to be connected to a soure of electrical energy,

output terminals to which said charging current is applied and adapted to be connected to a battery to be charged;

a switching device having switching means effectively connected between said input terminals and said output terminals and adapted in a -rst condition of said switching means to prevent charging current from being applied to said output terminals and in a second condition to enable charging current to be applied to said output terminals;

an electronic switching unit having control input terminals and connected to said switching device to control the operation thereof in accordance with the signal applied to said input terminals;

a timer which can be adjusted from an off position to any of various selected initial timing positions and then moves at a timed rate to said off position, y

said timer having a switch operated thereby and effectively connected between said input terminals and said output terminals to prevent charging current from being applied to said output terminals when said timer is in said of position,

said timer having a variable impedance adjusted thereby and effective when said timer is adjusted to be correspondingly varied;

a voltage reference device connected to a source of voltage and having a constant voltage drop thereacross;

and control circuit means connected to said voltage reference device, said Variable impedance, said cutput terminals and said input terminals of said electronic switching unit effective when said output terminals are connected to a battery to be charged and when said timer and said variable impedance are adjusted to a position bearing a fixed relation to the voltage output of the battery to be charged to aiect the input signal applied to the input terminals of said electronic switch unit in such a manner that said switching device is operated to cause said switching means to assume said second condition in which said source can be connected to said output terminals.

2. The battery charging apparatus of claim 1 in which there is a signal device and means for actuating the same when said switching means of said switching device assumes said second condition.

3. The battery charging apparatus of claim 1 in which the switching device is a relay and the switching means is a switch and in which the relay has an electrical actuator for moving said switch between two positions.

4. The battery charging apparatus of claim 3 in which the electronic switching unit is a transistor having its output terminals connected in series with the actuator of said relay.

5. The battery charging apparatus of claim 1 in which a load resistance is connected across the output terminals while the timer is being adjusted and is disconnected from the load terminals when said switching means of said switching device assumes said second condition.

6. The battery charging apparatus of claim 1 in which said timer has an additional switch which is actuated when said timer is adjusted for the maximum timing period and in which a circuit controlled by said additional switch is established to said switching device independently of said control circuit means when the timer is adjusted for the maximum timing period without said switching device having been operated by said control circuit means.

References Cited UNITED STATES PATENTS 2,431,707 12/1947 Pugh 320-38 X 2,432,069 12/1947 Pugh 32C-38 X 3,178,629 4/1965 Saslow 320-30 X 3,200,303 8/1965 Maxwell 307-141 X 3,246,182 4/1966 Hanchett 307-141 3,388,566 6/1968 Kaper et al. 307-141 X JOHN F. COUCH, Primary Examiner STANLEY WEINBERG, Assistant Examiner U.S. Cl. X.R. 

